Simple HTML Sanitizer

htmlInterpolation.scala

object HTMLInterpolation {

  // definition of tagged type
  type Tagged[U] = { type Tag = U }
  type @@[T, U] = T with Tagged[U]

  trait Sanitized

  // use tagged type to express sanitized string
  type SanitizedString = String @@ Sanitized
  private def sanitized (s: String): SanitizedString = s.asInstanceOf[SanitizedString]

  implicit class HTMLContext (sc: StringContext) {
    def html (args: SanitizedString*): SanitizedString = {
      sanitized(sc.s(args:_*))
    }
  }

  import scala.language.implicitConversions

  implicit def autoStringSanitizer (string: String): SanitizedString = {
    sanitized(string
                .replaceAll("&", "&")
                .replaceAll("<", "&lt;")
                .replaceAll(">", "&gt;")
                .replaceAll("\"", "&quot;")
                .replaceAll("'", "&#39;"))
  }

  implicit def autoIntSanitizer (n: Int): SanitizedString = sanitized(n.toString)
  implicit def autoLongSanitizer (n: Long): SanitizedString = sanitized(n.toString)
  implicit def autoDoubleSanitizer (d: Double): SanitizedString = sanitized(d.toString)
}

// usage
object Main {
  def main (args: Array[String]): Unit = {
    import HTMLInterpolation._

    val a = html"<div>${"<script>alert(\"hello!\");</script>"}</div>"

    println(a)

    val b = html"<div>$a</div>"

    println(b)
  }
}